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The National Map Basemap Caches on Mobile iOS


There are two ways to use TNM basemaps on mobile iOS: Galileo and Mobile Atlas Creator (MOBAC).

Galileo Offline Maps

Galileo is a mapping/land-navigation application that has implemented USGS The National Map basemap data web services for iOS mobile devices (iPhone or iPad). Galileo can be loaded from iTunes for free; however the ability to record a GPS track costs a couple of dollars.

To use TNM basemap caches on iOS:

  1. Install the Application.
    1. Search "Galileo Offline Maps" in iTunes/App Store.
    2. Open the app by clicking on the icon on the iOS desktop.
    3. At the prompt: "Galileo would like to use your current location", select OK. This will enable the GPS tracking feature of the application.
    4. The initial map source will be OpenStreetMap.
  2. Import USGS The National Map (TNM) Data into Galileo.
    1. Open the Safari browser on the iOS device and navigate to
    2. Click any of the three links on the Galileo blog web page to create a direct feed of that map source into Galileo. For this example, select "USGS National Map - Topo".
    3. A new browser window will appear. Select: "Open in Galileo". (Note: If the file size is 0 bytes, hit the refresh button to reload the file. Then select "Open in Galileo".)
    4. The Galileo app will reopen. However, the initial view or zoom may be "too close" to show TNM map source (the most detailed TNM map tiles are at 1:18,000 scale). In this case, "pinch to zoom" out on the screen of the iOS device to zoom out, allowing TNM tiles to appear in the application (if a white grid is shown, the app may be zoomed in too far). Notice the scale bar on the lower left of the images to the right.
    5. The Galileo application will cache map tiles to wherever the application has browsed. Users only have to examine where the TNM map tiles will be stored on the local device. This will allow the tiles to be "disconnected" from the internet and be used a remote location. Note: Under Settings/Cache Info, users can view how many tiles have been stored.
  3. Test the Offline Map Caches.
    1. Select the application's sprocket icon.
    2. Under Settings/Network Mode, select "Offline" (rather than WiFi+3G or WiFi).
    3. Zoom out to see the limitations of cached map data.
    4. Areas will be available which were previously viewed online. However, images may be low resolution or unavailable when zooming into a location that hasn't been previously viewed online.

Mobile Atlas Creator (MOBAC)

The Mobile Atlas Creator (MOBAC) is a desktop application that provides the ability to develop map caches for many different apps, including AlpineQuest for Droid and Galileo for iOS. MOBAC works on Mac and Windows desktops. The map caches from MOBAC elimiate the need for users to navigate everywhere in Galileo to cache the map tiles (which is time consuming and may not grab all of the required map tiles). Instead, MOBAC collects all of the tiles in one process.

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Disclaimer: Any use of trade, firm or product names does not imply endorsement by the U.S. Government. No warranty, expressed or implied, is made by the USGS or the U.S. Government as to the accuracy and functioning of the commercial software programs cited in this Technical Announcement, and the U.S. Government shall not be held liable for improper or incorrect use of The National Map topographic data from USGS.